The present invention relates generally to the field of integrated circuits and, in particular, to integrated circuits using high aspect ratio vias through a semiconductor wafer and method for forming same.
Integrated circuits are used in a wide range of applications. Integrated circuits are conventionally formed on a wafer of semiconductor material. In order to function properly, the integrated circuit uses various electronic signals that are generated or provided from a source that is external to the integrated circuit, e.g., timing or xe2x80x9cclockxe2x80x9d signals, and power supply signals.
To connect to these signals, the integrated circuit includes a number of bond pads that are typically formed on the surface of the integrated circuit. The bond pads are coupled to nodes of the integrated circuit that need to receive the specified signals. Further, the bond pads are coupled to the external sources by leads. The leads are connected to the bond pads through bond wires. Conventionally, the bond wires have an arc-like shape that extends outwardly from the surface of the semiconductor substrate. The size, shape and length of these bond wires can hamper the operation of some integrated circuits due to the high resistance and high self inductance of the bond wires.
Mixed mode circuits are one type of circuit that can benefit from low impedance connections between bond pads and leads. A mixed mode circuit is a circuit that includes both an analog circuit and a digital circuit that are formed on the same semiconductor wafer. The mixed mode circuits can benefit from low impedance connections to a ground bus and a guard ring to suppress noise in the analog circuits that is caused by the high speed switching of the digital circuits. Such mixed mode circuits are now being used in microprocessors, memory devices, and other integrated circuits.
High inductance or high impedance connections between bond pads and leads can also introduce noise into the power distribution system of an integrated circuit. For example, high speed synchronous digital circuits require large switching currents. The large switching currents can introduce noise into the power distribution system of the digital circuit when the inductance or impedance of the connections to the power supply and ground busses is too high.
Similarly, circuits that include output drivers with large transient currents also can benefit from low resistance and low inductance connections to various power supply, ground, clock and guard ring busses.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for low impedance, low inductance contacts or connections to power supply, ground, clock, or guard ring buses in integrated circuits.
The above mentioned problems with integrated circuits and other problems are addressed by the present invention and will be understood by reading and studying the following specification. Integrated circuits are described which use high aspect ratio vias through a substrate that are filled with a conductive material using a substitution technique so as to create low impedance, low inductance connections between various busses and selected leads. Advantageously, such high aspect ratio vias can be used to reduce problems such as ground bounce, substrate bounce, power supply noise, simultaneous switching noise, and cross talk between analog and digital circuits in mixed mode circuit by allowing the signals to be distributed on the back side of the substrate, away from the components of the integrated circuit.
In particular, an illustrative embodiment of the present invention includes an integrated circuit and a method for forming the same. The integrated circuit includes a semiconductor wafer with first and second surfaces. A functional circuit is formed on the first surface of the semiconductor wafer. Further, a metallization layer is formed outwardly from the first surface of the semiconductor wafer. The integrated circuit also includes at least one high aspect ratio via that extends through the layer of semiconductor material. This via provides a connection between a lead and the functional circuit.
In another embodiment, a method for forming an integrated circuit is provided. The method includes forming a functional circuit in a first surface of a semiconductor wafer. At least one high aspect ratio hole is formed through the semiconductor wafer from the first surface to a second, opposite surface. The at least one high aspect ratio hole is filled with polycrystalline semiconductor material and a layer of conductive material is deposited on the first and second surfaces of the semiconductor wafer. The semiconductor wafer is annealed such that the conductive material replaces the polycrystalline semiconductor material to form low resistance and low inductance conductors in the at least one high aspect ratio hole. At least one contact pad is formed on the second surface of the semiconductor wafer so as to provide a contact for the conductors in the at least one high aspect ratio hole.
In another embodiment, an integrated circuit is provided. The integrated circuit includes a semiconductor wafer. A functional circuit is formed in one surface of the semiconductor wafer. A number of high aspect ratio vias are formed through the thickness of the semiconductor wafer. A first end of each high aspect ratio via is coupled to a metallization layer on the first surface of the wafer. A second end of the high aspect ratio via is coupled to a bond pad on a second, opposite side of the semiconductor wafer. The integrated circuit also includes a chip carrier. The chip carrier has leads disposed on a surface of the chip carrier that are coupled to selected of the bond pads on the second surface of the semiconductor wafer when the semiconductor wafer is disposed on the chip carrier.
In another embodiment, a method for forming an integrated circuit is provided. The method includes forming a functional circuit in a first surface of a semiconductor wafer. A number of etch pits are formed in the first surface of the semiconductor wafer at selected locations in the functional circuit. An anodic etch of the semiconductor wafer is performed such that high aspect ratio holes are formed through the semiconductor wafer from the first surface to a second, opposite surface at the location of the etch pits. An insulating layer is formed on an inner surface of each high aspect ratio hole. The high aspect ratio holes are filled with polysilicon. A layer of aluminum is sputter deposited on the first and second surfaces of the semiconductor wafer and the semiconductor wafer is annealed at a temperature of approximately 500 degrees Celsius. The aluminum replaces the polysilicon to form conductors in the high aspect ratio holes. A number of contact pads are formed on the second surface of the semiconductor wafer so as to provide contacts for the conductors in the high aspect ratio holes.